A conventional spark plug used in an internal combustion engine has a metallic shell adapted to be fitted into an opening in communication with a cylinder. The shell accommodates a ceramic or other dielectric body through which extends a first electrode. One end of the electrode is coupled to an ignition system, whereas the other end of the electrode terminates in a tip which is exposed to combustible vapors present in the cylinder. A second electrode or ground wire has one end thereof overlying the tip of the first electrode and is spaced therefrom to provide a gap of predetermined size. The ground wire is bent between its ends and has its other end secured to the shell.
The gap between the electrode tip and the ground wire is variable, but it usually is preset to provide the most efficient fuel ignition when the engine is at normal operating temperature. For example, the spark gap may be set at about 0.045 inch which provides for good ignition when the engine is hot. When the engine is cold, however, it is more difficult to generate a spark between the electrode tip and the ground wire than is the case when the engine is hot. Consequently, it is more difficult to start a cold engine than a warm engine.
An object of the invention is to provide a spark plug which overcomes or minimizes the difficulty in starting cold engines, but without detracting from the efficiency of the engine when it is at operating temperature.